Baslow PCC

Flood Risk Assessment & Surface Water Drainage Strategy

Prepared by

Matthew Glover

for

Prime (UK) Developments Ltd

Hydrock Ref: R/10055/001

May 2010 Hydrock Consultants Ltd Over Court Barns Almondsbury Bristol BS32 4DF

Tel: 01454 619533 Fax: 01454 614125

Client: Prime (UK) Developments Ltd

Project: Baslow PCC

Title: FLOOD RISK ASSESSMENT & SURFACE WATER DRAINAGE STRATEGY

Date: May 2010

Copy No.: 1

| Issue | Purpose/Status | Prepared by | Checked | Approved | Date | |-------|----------------|-------------|---------|----------|------------| | A | FINAL | MG | KT | DL | MAY 2010 | | - | DRAFT | MG | KT | DL | APRIL 2010 |

Hydrock Consultants has prepared this report in accordance with the instructions of the above named Client for their sole and specific use. Any other persons who may use the information contained herein do so at their own risk. CONTENTS

1.0 INTRODUCTION 2.0 SITE DESCRIPTION AND EXISTING SITE DRAINAGE 3.0 DEVELOPMENT PROPOSALS 4.0 SURFACE WATER RUN-OFF PROPOSALS 5.0 CONSIDERATIONS OF FORMS OF FLOODING 6.0 CONCLUSIONS

APPENDICES

A LOCATION PLAN & PROPOSED SITE LAYOUT AND DRAINAGE STRATEGY B SITE TOPOGRAPHICAL SURVEY C SEVERN TRENT WATER – PUBLIC SEWER RECORD PLAN D ENVIRONMENT AGENCY PLAN E WINDES GREEN FIELD CALCULATIONS & SW STORAGE SIMULATION 1.0 INTRODUCTION

1.1 Hydrock Consultants have prepared this Flood Risk Assessment on behalf of Prime (UK) Developments Ltd in support of the development of a new primary care centre in Baslow on a site off Cock Hill Road, Derbyshire.

1.2 The site is approximately 0.325Ha and is located in the centre of Baslow.

1.3 The existing site consists of grassland and dense vegetation.

1.4 The Environment Agency, the Local Authority and Seven Trent Water have been contacted as sources of information in preparation for this report.

1.5 The Environment Agency flood plain map indicates that the site is wholly within a zone 1 flood risk area which has a probability of flooding of less than 1 in 1000 year flood event (i.e. an annual probability of flooding of less than 0.1%), see Appendix D.

1.6 The site therefore satisfies the requirements for BREEAM POL 5 “Flood Risk” and gains 2 credits due to the low probability of flooding as it is in Zone 1.

1.7 This report has been produced in accordance with PPS25 (Planning Policy Guidance Statement 25 Development and Flood Risk) and assessed the flood risks of the proposals and surface water run-off implications of the development.

1.8 This Flood Risk Assessment considers:

- the existing drainage regime
- the various potential flooding mechanisms acting on the site
- storm water drainage to manage surface water run-off 2.0 SITE DESCRIPTION AND EXISTING SITE DRAINAGE

2.1 The site is bounded to the south by an existing bowling green and to the west is an access road which leads onto Church Lane. North of the site is an electricity sub-station and along the northern boundary is a dense row of trees. Dense trees also bound the north west area of the site, to the east of the site are residential houses and open green fields.

There is a grass bank approximately 0.7m high that runs along the boundary of the northern part of the bowling green which then runs through the site towards the east. The site is generally flat with levels ranging between approximately 113.00m AOD and 112.40m AOD, see Appendix B.

2.2 The main watercourse is the River Derwent which is located approximately 225 meters to the West of the site which flows in a southerly direction. There is also the Bar Brook a tributary to the Derwent which is approximately 230 meters to the East. This has its confluence with the Derwent some 1000m to the south of the site.

2.3 Severn Trent Water sewer records show that there is a 150mm diameter public foul water sewer in Church Lane which flows to the north west. The is also a 225mm diameter public surface water sewer approximately 150m to the north west located at the roundabout of Church Lane. To the east of the site approximately 230m there is a 375mm diameter public surface water sewer which outfalls into the Bar Brook watercourse which eventually joins the River Derwent to the south. See Appendix C. 3.0 DEVELOPMENT PROPOSALS

3.1 The proposed development will consist of one 2 storey building to the south eastern part of the site. There will be a new access road with associated car parking and soft landscaping. See Appendix A.

3.2 It is proposed that the total developed impermeable area will be approximately 68% of the site (0.222Ha) with the remaining areas as soft landscape. 4.0 SURFACE WATER RUN-OFF PROPOSALS

4.1 The disposal of Surface Water Run-off is to be in accordance with the Planning Policy Statement (PPS25). Surface Water arising from a developed site should, as far as practicable, be managed in a sustainable manner to mimic the surface water flows from the site prior to the proposed development. Therefore a number of options have been considered in turn and are addressed below.

4.2 Rainwater Harvesting Techniques (BREEAM - WAT 5)

The use of Rainwater harvesting systems is becoming increasingly common and potentially offers long term cost savings and environmental benefits. Rainwater harvesting systems from the roof runoff can be used for grey water uses such as toilet flushing and irrigation of the proposed landscaped areas.

It is therefore recommended that consideration be given to the use of Rainwater Harvesting systems given that the space to accommodate such a system is available and that, as part of the BREEAM Assessment WAT 5 “Water Recycling” for the building, this represents a potential additional 2 Credits.

It should be noted that the provision of rainwater harvesting attenuation is not considered to offer any reduction in the contributing area to any final drainage solution as it is standard practice to consider that the attenuation system is full at the time of any design storm occurrence.

4.2 Soakaway & Infiltration Techniques

A Desk study was carried out by Applied Geology (Report AG1293-10 dated April 2010) suggests that the site geology is likely to be underlain by Alluvium which is associated with the River Derwent overlying Ashover Grit (Sandstone). No infiltration tests as yet have been carried out. For the purpose of the drainage strategy it has been assumed that the implementation of soakaways will not be feasible (until otherwise confirmed by infiltration testing).

4.3 Attenuation & Storage Techniques

On the assumption that the use of soakaways is deemed inappropriate for the site consideration has been given to attenuation and storage methods.

Runoff from the existing green field has been calculated to be 0.7 l/s using Micro Drainage Wides ICP SUDs method, see Appendix E. Severn Trent Water discharge rate requirements for green field site are 5l/s/ha, which results in a predicted discharge rate of 1.6l/s for the site. However, based on the minimum discharge required to prevent blockage of control devices this is increased to a rate of 5l/s as per Severn Trent guidelines.

It has been proposed that a discharge rate of 5 l/s from the new development will be pumped into the existing public combined water sewer in Church Lane. Severn Trent has stipulated that the disposal of surface water by means of soakaways should be considered as a primary method. If this is not practical and no watercourse is available, then discharge to sewers should be considered. In order to confirm a proposed discharge rate of 5l/s computer modelling of the combined sewer will need to be carried out by Severn Trent Water to determine if any works will be required to the public system regarding capacity. Refer to Appendix C for Severn Trent Water correspondence.

It is proposed to attenuate the surface water runoff up to the 1 in 100 year return period with an allowance for 20% climate change.

Storage requirements based on a restricted discharge rate have been assessed and an approximate storage volume of 41m³ is expected for the 1 in 30 year design. If storage is to accommodate the 1 in 100 year + 20% climate change then it is estimated that a volume of 80m³ will be required. Part of this storage can be incorporated into the pumping station. This will need to be confirmed at the detailed design stage if it is to offset against the proposed storage system, see Appendix A.

The use of buried attenuation systems, including oversized pipes, storage crates and tanked permeable paving, may be a required and the location and access to maintain any system will need to be considered within the detailed design stage.

The application of a tanked permeable paved system which will discharge into the surface water network system has been considered. This offers a water quality improvement from trafficked areas and addresses any potential associated contamination. Alternatively, if the area is to have impermeable surfacing then the application of petrol/oil separators may be required to service the parking areas. Following consultation with Severn Trent Water and the Environment Agency both design methods could satisfy BREEAM POL 6 – “Minimising Watercourse Pollution” and therefore gain an additional 1 credit.

4.4 Positive Unrestricted Discharge

It is deemed not appropriate in accordance with PPS25 to consider a direct positive unrestricted discharge to any existing adopted public sewer or watercourse unless it can be demonstrated that such discharge is less than that of the previous development. As there is an increase in impermeable area a free discharge would not be acceptable. 4.6 Construction of Surface Water Management Scheme

It is recommended that the appointed contractor identify a proposed method of construction for approval of the surface water retention and discharge prior to commencement of works. This is to prevent any contamination or silt build up occurring (on off-site areas including footways and carriageways) which could potentially enter the existing adopted public sewer networks in the area during the construction phase.

4.7 Designing for Exceedance

As identified in CIRIA C635: “Designing for exceedance in urban drainage – Good practice” it is important to consider within the initial and design stages of any project the implications and methods for addressing design exceedance. This report identifies a number of ways which this can be addressed.

All drainage forming the surface water network as part of this development are to be designed in accordance with the Environment Agency’s Design Advice.

In the event of design exceedance or system failure consideration has been given to design levels and overland flooding routes (Section 4, CIRIA C635). These are identified on the proposed drainage layout plans in Appendix A. The routes form part of the proposed and existing road, parking areas and footpath access routes around the building. Recharging of the proposed surface water sewer network should be considered during detailed design including the use of permeable paving attenuation in parking areas or direct drainage connections.

Application of these proposals are seen to offer a significant benefit under PPS25 and CIRIA 635 to the downstream surface water network initially by the application of attenuation and a SUDs approach but also from the reduction of discharge/runoff rates and their extension over a longer time period which should aid/reduce potential network failures further downstream of the site. 5.0 CONSIDERATION OF FORMS OF FLOODING

5.1 Fluvial

The nearest watercourse to the site is the River Derwent which is located 225 miles to the west of the site. There is also the Bar Brook which flows towards the south some 230m to the east of the site. However, given the relative levels of the site to the floodplain, and its distance away from both watercourses, the site is not considered to be at risk of fluvial flooding from these sources.

The site is confirmed to be in flood Zone 1 which is assessed as having less than a 1 in 1000 year probability of river or sea flooding in any year (\<0.1%). All land uses are considered appropriate in this zone, see Appendix D.

5.2 Tidal

Due to the site location and topography it is considered not at risk from Tidal flooding.

5.3 Surface Water

Potential overland flooding routes (from, for example, capacity exceedance elsewhere) through the site from any surface water flows (should they occur) would be from the small green north of the site. However, the site detail levels will ensure that the potential of flooding to the building is low. The site is therefore not considered to be at risk from surface water flooding.

5.4 Ground Water

According to the ground vulnerability map obtained from the Environment Agency, the site is located in a minor aquifer zone. In addition as the site is not within a topographical hollow it is not considered to be at risk from groundwater flooding.

5.5 Sewers

Severn Trent Water Sewer Records indicate that there is a combined water sewer that runs through Church Lane (North of the site) and flows to the west. Severn Trent has confirmed that there are no records of flooding within Church Lane. However, there have been recorded incidents of flooding in the fields downstream in one part of the upstream area.

The strategic flood risk assessment (SFRA) for the Peak District National Park Authority highlights that the area is at medium risk of flooding from sewers, according to the DG5 register 10 properties have flooded from sewers. If any flooding was to occur from these sewers the flow would be directed down the existing access off Church Lane which will serve the existing bowling green and the new primary care centre. Design levels will ensure that flooding from the combined sewer in Church Lane would be directed away from the site. Therefore, the site is not considered to be at risk from sewer flooding.

6.0 CONCLUSIONS

6.1 The site is confirmed to be within flood risk Zone 1 as indicated on the Environment Agency indicative flood plain maps and therefore has a low probability of flooding from tidal and fluvial sources.

6.2 The site is also concluded to have a low probability of flooding to, and from, the local catchment provided a suitable sustainable urban drainage scheme is employed.

6.3 The development therefore satisfies the requirements for BREEAM POL 5 - "Flood Risk" for 2 credits due to the low probability of flooding in a Zone 1.

6.4 Consideration should be given to the use of Rainwater Harvesting techniques in the development as this would form part of the BREEAM Assessment WAT 5 - "Water Recycling" for the building and gain an additional 2 credits.

6.5 It has been assumed that the use of soakaways is not considered viable until infiltration testing onsite can confirm otherwise.

6.6 Should soakaway systems prove impracticable, then the use of permeable paving with tanked storage to improve the water quality of the discharge should be considered in the final detailed design or alternatively the use of Petrol / Oil Separators to satisfy BREEAM POL 6 - "Minimising Watercourse Pollution" as this would gain an additional 1 credit.

6.7 Although the proposed discharge rate should restrict the proposed runoff to mimic the green field conditions, because the predicted rate of 1.6 l/s Severn Trent guidance suggests a minimum discharge rate of 5l/s to prevent blockage of control devices. Severn Trent Water has requested a sewer capacity check, to confirm that the existing sewer network can accommodate the proposed discharge rate. Refer to Appendix C for correspondence.

6.8 Preliminary storage requirements based on the proposed impermeable area of 0.222 ha and the restricted discharge rate of 5l/s for up to the 1 in 100 year design storm with an allowance for 20% climate change has been assessed using WinDes. Approximately 41m$^3$ of storage is predicted for the 1 in 30 year storm and 80m$^3$ of storage is required for the 1 in 100 year 20% climate change would be required. See Appendix A.

6.9 Final site design levels for the buildings & road layout should consider local low points and identify the potential overland flooding routes. 6.10 It is recommended that the construction run-off mitigation methods be employed during initial site start up.

6.11 Designing for Exceedance (Section 5.7) has been considered and overland flood flow routes identified. Appendix A

LOCATION PLAN

PROPOSED SITE LAYOUT & DRAINAGE STRATEGY FOR THE 1 IN 100 YEAR + 20% CLIMATE CHANGE Appendix B

SITE TOPOGRAPHICAL SURVEY Appendix C

SEVERN TRENT WATER - PUBLIC SEWER RECORD PLAN

SEVERN TRENT WATER CORRESPONDENCE Hydrock Over Court Barns Over Lane Almondsbury Bristol BS32 4DF

F.A.O: Matthew Glover

12th May 2010

Dear Sir/Madam

Land off Church Lane, Baslow, Derbyshire Proposed Primary Care Centre (425533, 372066).

I refer to your recent Development Enquiry Request in respect of the above site. Please find a copy of the sewer records and ‘Additional Guidance Notes’ enclosed for your information.

Foul Water Drainage

The foul discharge from the care centre can be accommodated based on being less than 1 l/sec.

The 225mm dia combined sewer in Church Lane has been calculated to have between 17 l/sec and 40 l/sec design capacity depending on the gradient at each length of sewer pipe. Desk top calculations suggest that a max foul discharge from the upstream catchment area is approximately 6.5 l/sec, including the hotel, two public houses and 2 restaurants, this does not include the surface water element (please see below). Part of the upstream foul / combined flow is pumped via the sewage pumping station in the Church Lane car park to the east of the development site. I have assumed that this will pump at a rate of around 6 - 12 l/sec. The pumping rate of this station is being investigated at present to get a more accurate figure in due course.

Surface Water Drainage

Under the terms of Section H of the Building Regulations 2000, the disposal of surface water by means of soakaways should be considered as the primary method. If this is not practical and no watercourse is available as an alternative, the use of sewerage should be considered. In addition, other sustainable drainage methods should also be explored before a discharge to the public sewerage system is considered.

If these are found to be unsuitable, satisfactory evidence will need to be submitted. The evidence should be either percolation test results or a statement from the SI consultant (extract or a supplementary letter). I understand that test results will be forthcoming in due course.

The River Derwent is approximately within 200 metres to the west of the site; discharging surface water from the site to the river should be explored before a pumped disposal to the public combined sewer is agreed. There is also a highway drain in Church Lane (A6190) within approximately 120 metres to the west of the site. It may be possible to agree with the Highway Authority to drain surface water from the access road and car park to the highway drain rather then to the combined sewer.

When this information is made available a decision will be made on the permitted surface water discharge.

In reference to the desk top calculations for the foul discharge in the upstream area above; further calculations based on GIS mapping information, aerial photographs and the information from public sewer records were carried out regarding possible surface water flows within the catchment area upstream. Assumptions were made regarding which impermeable areas are likely to discharge to the public combined sewers, public surface water sewers and highway drains, I have concluded that there is one section of the public combined sewer in Church Lane that is either at capacity or very close to capacity in times of significant storm flows.

Although no flooding is presently known in Church Lane itself, there have been incidences of flooding in the fields downstream adjacent to the treatment works and of foul flooding in one part of the upstream area. On this basis, I feel that if a discharge of surface water is to be made to the public combined system the client should consider commissioning Severn Trent to carry out computer modelling of the combined sewerage system in Church Lane to ascertain if the system will be adversely affected by an extra 5 l/sec and what works may be required to the public system regarding capacity or storage. Any flows generated by the site in excess of the permitted discharge rate will have to be attenuated within the development site.

For any new connection(s) into the public sewer network or the reuse of an existing sewer connection(s), you will need to apply under Section 106 Water Industry Act 1991 as amended by the Water Act 2003. Our New Connections Team currently processes Section 106 applications, please contact them on 0116 234 3320 for an application pack and guidance notes (or visit www.stwater.co.uk). For the avoidance of doubt, it is suggested that you quote the reference number above. Applications to make such connections should be made separately from any application for adoption of the related sewers under Section 104 Water Industry Act 1991 as amended by the Water Act 2003.

I must inform you that this evaluation is only valid for 6 months from the date of this letter. Please quote the reference number above, in all future correspondence.

Yours faithfully,

WF Walton Asset Protection Manager - East Waste Water Additional Guidance Notes

If you experience difficulty in the provision of off-site sewers to serve your proposed development, an application for requisition sewers under Section 98 Water Act 2003 may be appropriate on request to this office.

If there are existing public sewers within the curtilage of the development site that may affect the proposed development the option to divert them under Section 185 Water Act 2003 may be available. All costs incurred would lay with the applicant.

All potentially adoptable sewers must be designed and constructed in accordance with the guidelines in Sewers for Adoption (6th Edition), after 1st May 2006. A Severn Trent Water Addendum for Foul Sewage Pumping Stations will be available at www.wrcplc.co.uk/sfa.

Severn Trent Water applies a separate charge for each connection to the public sewerage system under Section 106 Water Act 2003. This is to cover our costs for administration and inspection of such connections. Applications to make such connections should be made separately from any application for adoption of the related sewers under Section 104 Water Act 2003. All such applications should be made to this office at the appropriate time.

In cases where the complexity of both the existing receiving sewerage system and the proposed additional sewerage necessitates the construction of a suitable computer model, Severn Trent Water can offer this service. Enquiries should be addressed to Mr. Jim Borrington of our Sewer Modelling Team on 01332 683430.

All enquiries with respect to the supply of sewer records only should be directed to Severn Trent Water Limited, Record Management Centre, Waterworks Road, Edgbaston, Birmingham, B16 9DD (Tel. 0845 601 6616).

Asset Protection Waste Water East Appendix D

ENVIRONMENT AGENCY FLOOD MAPS Appendix E

WINDES GREENFIELD RUNOFF CALCULATION

WINDES STORM WATER STORAGE SIMULATION ICP SUDS Mean Annual Flood

Input

| Return Period (years) | SAAR (mm) | Area (ha) | Soil | Urban | Region Number | |-----------------------|-----------|-----------|------|-------|---------------| | 2 | 889 | 0.325 | 0.300| 0.000 | Region 4 |

Results 1/s

- QBAR Rural: 0.8
- QBAR Urban: 0.8
- Q2 years: 0.7
- Q1 year: 0.7
- Q30 years: 1.5
- Q100 years: 2.0

### Summary of Results for 100 year Return Period (+20%)

Half Drain Time : 133 minutes.

| Storm Event | Max Level (m) | Max Depth (m) | Max Infiltration (l/s) | Max Control (l/s) | Max Outflow (l/s) | Max Volume (m³) | Status | |-------------|---------------|---------------|------------------------|-------------------|-------------------|-----------------|--------| | 15 min Summer | 99.322 | 0.622 | 0.0 | 5.0 | 5.0 | 38.6 | O K | | 30 min Summer | 99.517 | 0.817 | 0.0 | 5.0 | 5.0 | 50.7 | O K | | 60 min Summer | 99.676 | 0.976 | 0.0 | 5.0 | 5.0 | 60.5 | O K | | 120 min Summer | 99.742 | 1.042 | 0.0 | 5.0 | 5.0 | 64.6 | Flood Risk | | 180 min Summer | 99.727 | 1.027 | 0.0 | 5.0 | 5.0 | 63.7 | Flood Risk | | 240 min Summer | 99.694 | 0.994 | 0.0 | 5.0 | 5.0 | 61.7 | O K | | 360 min Summer | 99.621 | 0.921 | 0.0 | 5.0 | 5.0 | 57.1 | O K | | 480 min Summer | 99.546 | 0.846 | 0.0 | 5.0 | 5.0 | 52.5 | O K | | 600 min Summer | 99.471 | 0.771 | 0.0 | 5.0 | 5.0 | 47.8 | O K | | 720 min Summer | 99.397 | 0.697 | 0.0 | 5.0 | 5.0 | 43.3 | O K | | 960 min Summer | 99.260 | 0.560 | 0.0 | 5.0 | 5.0 | 34.7 | O K | | 1440 min Summer | 99.037 | 0.337 | 0.0 | 5.0 | 5.0 | 20.9 | O K | | 2160 min Summer | 98.843 | 0.143 | 0.0 | 5.0 | 5.0 | 8.9 | O K | | 2880 min Summer | 98.792 | 0.092 | 0.0 | 4.6 | 4.6 | 5.7 | O K | | 4320 min Summer | 98.768 | 0.068 | 0.0 | 3.4 | 3.4 | 4.2 | O K | | 5760 min Summer | 98.754 | 0.054 | 0.0 | 2.7 | 2.7 | 3.3 | O K | | 7200 min Summer | 98.745 | 0.045 | 0.0 | 2.3 | 2.3 | 2.8 | O K | | 8640 min Summer | 98.739 | 0.039 | 0.0 | 2.0 | 2.0 | 2.4 | O K | | 10080 min Summer | 98.735 | 0.035 | 0.0 | 1.7 | 1.7 | 2.1 | O K | | 15 min Winter | 99.405 | 0.705 | 0.0 | 5.0 | 5.0 | 43.7 | O K | | 30 min Winter | 99.630 | 0.930 | 0.0 | 5.0 | 5.0 | 57.7 | O K | | 60 min Winter | 99.823 | 1.123 | 0.0 | 5.0 | 5.0 | 69.7 | Flood Risk | | 120 min Winter | 99.923 | 1.223 | 0.0 | 5.0 | 5.0 | 75.9 | Flood Risk |

| Storm Event | Rain (mm/hr) | Time-Peak (mins) | |-------------|--------------|------------------| | 15 min Summer | 106.075 | 24 | | 30 min Summer | 71.559 | 37 | | 60 min Summer | 46.096 | 64 | | 120 min Summer | 28.671 | 112 | | 180 min Summer | 21.391 | 144 | | 240 min Summer | 17.249 | 176 | | 360 min Summer | 12.705 | 246 | | 480 min Summer | 10.222 | 312 | | 600 min Summer | 8.628 | 380 | | 720 min Summer | 7.507 | 446 | | 960 min Summer | 6.022 | 572 | | 1440 min Summer | 4.405 | 808 | | 2160 min Summer | 3.215 | 1132 | | 2880 min Summer | 2.568 | 1468 | | 4320 min Summer | 1.867 | 2196 | | 5760 min Summer | 1.487 | 2936 | | 7200 min Summer | 1.246 | 3624 | | 8640 min Summer | 1.080 | 4376 | | 10080 min Summer | 0.957 | 5128 | | 15 min Winter | 106.075 | 24 | | 30 min Winter | 71.559 | 37 | | 60 min Winter | 46.096 | 64 | | 120 min Winter | 28.671 | 118 |

### Summary of Results for 100 year Return Period (+20%)

| Storm Event | Max Level (m) | Max Depth (m) | Max Infiltration (l/s) | Max Control (l/s) | Max Outflow (l/s) | Max Volume (m³) | Status | |-------------|---------------|---------------|------------------------|-------------------|-------------------|-----------------|--------------| | 180 min Winter | 99.901 | 1.201 | 0.0 | 5.0 | 5.0 | 74.5 | Flood Risk | | 240 min Winter | 99.856 | 1.156 | 0.0 | 5.0 | 5.0 | 71.7 | Flood Risk | | 360 min Winter | 99.746 | 1.046 | 0.0 | 5.0 | 5.0 | 64.9 | Flood Risk | | 480 min Winter | 99.628 | 0.928 | 0.0 | 5.0 | 5.0 | 57.5 | OK | | 600 min Winter | 99.508 | 0.808 | 0.0 | 5.0 | 5.0 | 50.1 | OK | | 720 min Winter | 99.393 | 0.693 | 0.0 | 5.0 | 5.0 | 43.0 | OK | | 960 min Winter | 99.183 | 0.483 | 0.0 | 5.0 | 5.0 | 29.9 | OK | | 1440 min Winter | 98.877 | 0.177 | 0.0 | 5.0 | 5.0 | 11.0 | OK | | 2160 min Winter | 98.784 | 0.084 | 0.0 | 4.2 | 4.2 | 5.2 | OK | | 2880 min Winter | 98.767 | 0.067 | 0.0 | 3.4 | 3.4 | 4.2 | OK | | 4320 min Winter | 98.749 | 0.049 | 0.0 | 2.5 | 2.5 | 3.0 | OK | | 5760 min Winter | 98.739 | 0.039 | 0.0 | 2.0 | 2.0 | 2.4 | OK | | 7200 min Winter | 98.733 | 0.033 | 0.0 | 1.6 | 1.6 | 2.0 | OK | | 8640 min Winter | 98.728 | 0.028 | 0.0 | 1.4 | 1.4 | 1.8 | OK | | 10080 min Winter | 98.725 | 0.025 | 0.0 | 1.3 | 1.3 | 1.6 | OK |

| Storm Event | Rain (mm/hr) | Time-Peak (mins) | |-------------|--------------|------------------| | 180 min Winter | 21.391 | 156 | | 240 min Winter | 17.249 | 190 | | 360 min Winter | 12.705 | 266 | | 480 min Winter | 10.222 | 340 | | 600 min Winter | 8.628 | 410 | | 720 min Winter | 7.507 | 478 | | 960 min Winter | 6.022 | 604 | | 1440 min Winter | 4.405 | 814 | | 2160 min Winter | 3.215 | 1108 | | 2880 min Winter | 2.568 | 1468 | | 4320 min Winter | 1.867 | 2200 | | 5760 min Winter | 1.487 | 2896 | | 7200 min Winter | 1.246 | 3664 | | 8640 min Winter | 1.080 | 4408 | | 10080 min Winter | 0.957 | 5088 |

### Rainfall Details

| Parameter | Value | |----------------------------|----------------| | Rainfall Model | FSR | | Return Period (years) | 100 | | Region | England and Wales | | MS-60 (mm) | 19.000 | | Ratio R | 0.343 | | Summer Storms | Yes | | Winter Storms | Yes | | Cv (Summer) | 0.750 | | Cv (Winter) | 0.840 | | Shortest Storm (mins) | 15 | | Longest Storm (mins) | 10080 | | Climate Change % | +20 |

### Time / Area Diagram

| Time (mins) | Area (ha) | |-------------|-----------| | 0-4 | 0.074 | | 4-8 | 0.074 | | 8-12 | 0.074 |

Total Area (ha) 0.222 Model Details

Storage is Online Cover Level (m) 100.000

Cellular Storage Structure

| Depth (m) | Area (m²) | Inf. Area (m²) | Depth (m) | Area (m²) | Inf. Area (m²) | |-----------|-----------|----------------|-----------|-----------|----------------| | 0.000 | 65.3 | 65.3 | 1.400 | 0.0 | 113.1 | | 1.300 | 65.3 | 113.1 | | | |

Pump Outflow Control

Invert Level (m) 98.700

| Depth (m) | Flow (l/s) | Depth (m) | Flow (l/s) | Depth (m) | Flow (l/s) | Depth (m) | Flow (l/s) | |-----------|------------|-----------|------------|-----------|------------|-----------|------------| | 0.100 | 5.0000 | 0.900 | 5.0000 | 1.700 | 5.0000 | 2.500 | 5.0000 | | 0.200 | 5.0000 | 1.000 | 5.0000 | 1.800 | 5.0000 | 2.600 | 5.0000 | | 0.300 | 5.0000 | 1.100 | 5.0000 | 1.900 | 5.0000 | 2.700 | 5.0000 | | 0.400 | 5.0000 | 1.200 | 5.0000 | 2.000 | 5.0000 | 2.800 | 5.0000 | | 0.500 | 5.0000 | 1.300 | 5.0000 | 2.100 | 5.0000 | 2.900 | 5.0000 | | 0.600 | 5.0000 | 1.400 | 5.0000 | 2.200 | 5.0000 | 3.000 | 5.0000 | | 0.700 | 5.0000 | 1.500 | 5.0000 | 2.300 | 5.0000 | | | | 0.800 | 5.0000 | 1.600 | 5.0000 | 2.400 | 5.0000 | | |